Pelt boards and drying units are used in the pelt industry in the process of tanning pelts. The pelts, such as pelts from smaller mammals, preferably minks, foxes or the like, are stretched onto a pelt board for drying. Historically such pelt boards were made from solid wood, however, recently hollow pelt boards made of plastic have been used. Such hollow pelt boards are often made from two elongated half parts which together form a convex surface about a central axis. The half parts may be movable relative to one another for allowing the pelt board to collapse in order to simplify the removal of the pelts after drying. The pelt boards typically have a slightly conical shape from a bottom end to a top end. The pelts are stretched onto the pelt boards such that the cranium end of the pelt is located at the top end of the pelt board and the tail end of the pelt is located at the bottom end of the pelt board.
The pelt boards are often used together with a layer of fat absorbing material such as paper for absorbing fat from the pelt. The moist of the pelt is however removed using a drying unit for drying the pelts by means of a flow of air. For this purpose, the pelt board has a plurality of openings or apertures for allowing drying air to pass through the pelt board. Drying air is received at the bottom part of the pelt board and passes via the inside of the hollow pelt board through the pelt board and pelt. The drying air thus actively removes moist and water from the pelts and thus the total drying time is significantly reduced compared to using wooden pelt boards.
The pelt boards are typically placed in a drying unit for drying. The drying unit comprises a shallow box shaped unit defining an inner space and a blowing unit. The drying unit defines a top surface having a number of apertures. The pelt boards have a connecting element at the bottom end. The connecting element is received and arrested in the apertures. The blowing unit forces an airflow into the inner space and into the bottom end of the pelt boards via the apertures. Each drying unit typically has in the range of 25-100 apertures allowing a corresponding number of pelt boards and associated pelts to be dried. The drying units are often movable simplifying the transport of a plurality of pelt boards and allowing the drying to take place in a room having an increased ex-change of air.
Examples of such drying units may be found in the applicants own international applications WO 2005/026394 A1 and WO 2007/085269 A1, disclosing a method and drying unit for drying out the leather side of a pelt stretched out and fixed in this position on a pelt board, and, a device for performing complete—or partial emptying/filling of a drying aggregate with upstanding expansion pelt boards, respectively.
The use of forced convection in the form of a blower generating a stream of drying air through the pelts reduces the total drying time significantly compared to drying by means of solid pelt board relying entirely on natural convection. The drying time may be improved further by increasing the capacity of the blower to generate a more powerful stream of drying air. However, the applicant has found out that increasing the intensity of the drying air stream may lead to a too fast drying or over-drying of the pelt which may lead to a reduced quality of the pelt and/or formation of spots or marks on the pelt. There is thus a need for drying units capable of drying the pelts at a suitable drying intensity and leaving a small amount of residual moist.
Further, the applicant has found out that the classic drying units do not necessarily deliver the same amount of drying air through all of its apertures. By increasing the capacity of the blower and thereby increasing the flow velocities, the difference between the apertures becomes even more apparent. Having approximately the same flow of air is important since it will allow all of the pelts of a drying unit to be appropriately dried out. Otherwise the problem will arise where some of the pelts of a drying unit are over-dried while some are still moist. Thus, it is an object of the present invention to achieve technologies for allowing more efficient drying of pelts using a drying unit and to avoid the above-mentioned problem.